The present invention relates to a road surface frictional coefficient estimating apparatus for a vehicle which, in particular, shows an estimated road surface frictional coefficient (hereinafter referred to as “road surface μ”) to a driver to assist driving.
Recently, various control techniques for vehicles, such as traction control, braking force control, and torque distribution control, have been proposed and put in practical use. Most of those techniques employ a road surface μ for the calculation or correction of required control parameters, and it is required to estimate the road surface μ in order to execute such control with reliability.
Referring to the estimation of a road surface μ, various techniques have been proposed, in which a road surface μ is estimated based on vehicle motion parameters such as lateral acceleration and a yaw rate. For example, in JP-A-2001-039289, the present applicant has proposed a technique for estimating a road surface μ by comparing an actual yaw rate estimated by an observer with a yaw rate on the basis of a high-μ road calculated using a model of vehicle motion on a high-μ road and a yaw rate on the basis of a low-μ road calculated using a model of vehicle motion on a low-μ road.